An example of an overlay technology that might be featured in a Cisco SDN solution is VXLAN (Virtual Extensible LAN).
VXLAN is used for encapsulating Layer 2 Ethernet frames within Layer 4 UDP packets, allowing for the creation of virtual overlay networks that can span across various physical networks. This is particularly useful in data center environments for scaling virtualized environments and enabling multi-tenancy.
The other options provided (CDP, PAgP, VTP) are more related to traditional network protocols and not specifically overlay technologies in the context of SDN.